Much of the work in an automobile assembly line is still being done by men, because there are a number of parts that cannot be handled by a robot, it is necessary to respond flexibly to frequent process switching, and for various other reasons.
In a small parts assembly process, a transportation means for transferring automobile bodies is equipped with a parts trolley. The parts trolley moves in sync with the movement of an automobile body, and relatively small parts and tools are placed on the workbench of the parts trolley. Workers perform a series of procedure as described below. As the first procedure, the worker takes out parts placed on the workbench, moves to the parts mounting position, mounts the parts to the automobile body, and returns to the position of the parts trolley. As the second procedure, the worker takes out other parts and a tool from the workbench, moves again to the mounting position of the parts, mounts the parts to the automobile body using that tool, and again returns to the position of the parts trolley. As the third procedure, the worker takes out yet another tool, moves to the position where refastening is to be performed, performs fastening work, and moves back to the position of the parts trolley. As the fourth procedure, the worker pushes the parts trolley back to the original position, namely the initial position. In the assembly line where a series of procedure described above is performed, no parts shelves are provided to reduce the walking distance of workers. In another example of automobile assembly lines, robots are installed in specified positions instead of workers to promote automation of the assembly line.
Research and development on robots capable of working together with human workers has been performed (Patent Literatures 1 to 5). The robot arm control technique disclosed in Patent Literature 1 allows even a multiple-joint robot arm to contact workers safely. The optimum contact motion corresponding to the movement of workers does not cause contact damage to workers. With the technique disclosed in Patent Literature 2, the minimum output necessary for a robot to perform a specified work is obtained, and by controlling the output exceeding that limit, co-existence and cooperation between the robot and the worker are ensured. With the technique disclosed in Patent Literature 3, the movable range of a robot and a worker off-limit area are established accurately and in simple procedure, and the movable range and the off-limit range can be modified as required. The technique disclosed in Patent Literature 4 prevents the robot from entering into a prohibited area unexpectedly due to a human error that may occur during cooperative work of the worker and the robot, while ensuring that the movement of the robot is not controlled carelessly. With the technique disclosed in Patent Literature 5, a robot, working with humans and having a joint portion, that may contact the worker during motion, is provided with a contact sensor. Receiving a detection signal from the contact sensor, the control means controls the drive unit to perform risk aversion operation, thus preventing harm to workers.
In addition to techniques described above, with the transfer robot system disclosed in Patent Literature 6, a robot arm is mounted to an unmanned carrier, which is transferred between facilities, with the robot arm made to perform necessary work.